Method and apparatus for roll-extruding large diameter thin-walled tubing



3 Shsets-Sheet 1 AW CLAU6 1. Sponcz C. L. SPORCK DIAMETER THIN-WALLED TUBING I i Lww m m June 30, 1970 METHOD AND APPARATUS FOR ROLL-EXTRUDING LARGE Filed July 9, 1968 Q I: M I Na c. L. SPORCK 3,517,535 METHOD AND APPARATUS FOR ROLL-EXTRUDING LARGE June 30, 1970 DIAMETER THIN-WALLED TUBING 3 Sheets-Sheet 2 Filed July 9, 1968 Fl G. 5 8

CLAUS L. SPOZK 5; %M

June 30, 1970 c. L. SPORCK 3,517,535

METHOD AND APPARATUS FUR ROLL-EXTRUDING LARGE DIAMETER THINWALLED TUBING 3 Sheets-Sheet 5 Filed July 9, 1968 United States Patent O 3,517,535 METHOD AND APPARATUS FOR ROLL-EXTRUD- ING LARGE DIAMETER THIN -WALLED TUBING Claus L. Sporck, Traverse City, Mich., assignor to Parsons Corporation, Traverse City, Mich., a corporation of Michigan Filed July 9, 1968, Ser. No. 743,553 Int. Cl. B21b 19/16 US. C]. 72-85 8 Claims ABSTRACT OF THE DISCLOSURE Relatively large diameter thin-walled tubing is roll-extruded from a generally cylindrical billet by a new method and apparatus, in part utilizing that type of power tooling having a power driven mandrel rotating between radially inward directed pressure rolls which are drawn axially by a lead screw. The torque of rotation is supplied at one end of the billet at which the extruding commences. Simultaneously, pressure cylinders apply axial tension to the billet through a bearing collar at its opposite end. This makes it possible to roll extremely thin-wal1ed tubing without irregularities from localized stresses beneath the rolls.

BACKGROUND OF THE INVENTION Tubular billets of metal have heretofore been formed by a roll-extruding process, in which pressure rolls, directed radially inwardly, are advanced axially as the rolling progresses. With such equipment the billet may be thinned along its entire length. By repetition of the process, a long, thin-walled tube may be gradually developed.

Prior to the present invention, the procedure usually followed was to secure such a metal billet to the mandrel at the end at which the mandrel was supported by the machine tool; and to set the pressure rolls and lead screw so that they commenced working at the opposite end of the billet and proceeded to thin the metal as they progressed toward the supported end. Accordingly, the driving torque would be transmitted through the thicker portion of the billet to the point of thinning; beyond this point the material would not be subject to torsional stress. However, the thinned material could escape from the advancing forming rolls only by passing under them, to elongate the billet in the axial direction opposite the direction in which the rolls were progressing.

SUMMARY OF THE INVENTION The present invention provides a method and apparatus for forming such a tubular billet into a relatively large diameter, precisely thinned tube, characterized by uniformity of thickness, high strength, and freedom from irregularities.

In the method of the present invention, as generally summarized, the lead screw of the machine tool is set to move the axial position, or station, of the forming rolls in the same direction toward which the billet is to be extruded by the pressure rolls. In the illustrated embodiment of the method, a billet is used which has a closed or otherwise constricted end, machined to such internal diameter as will fit smoothly over the mandrel. The billet is then fitted thereon and its end is engaged to the mandrel by an air tight seal, as by means of an annular resilient ring, inward of which air is evacuated, and through which the torque of the tool is applied to the billet. Regardless of how the torque is so applied to one end of the billet, its opposite end is grasped by a collar which is free to rotate; and forces are applied to the collar equivalent to an axial tension force on the billet.

As rotative power is applied to the mandrel, the forming rolls, pressing radially inward with enough force to extiude the wall of the billet, are advanced by the lead screw from the end of the billet so engaged by the mandrel, toward the end grasped by the free-rotating collar. As the rolls progressively extrude the material along the length of the billet, the tension force acts through the portion not yet thinned by the rolls, to draw the material at the points of Working so that the direction of extrusion is axial.

The pressure rolls are first set to thin the billet by a fixed increment, moving the material axially and thereby increasing its length. On repeating the steps with the rolls readjusted inward to thin it in further increments, a long tube is formed of desired wall thickness. The tension force applied to the wall, so thinned, is less than would stress it to its yield point in tension. Nevertheless the tension overcomes local effects at the rolls which would tend to buckle the material being forced, including friction against the surface of the mandrel, and also the tendency of the thinned wall to buckle from the driving torque, resisted locally at the forming rolls.

As applied to a tool of the type described, my invention embraces the use of a conventional type tool including a powered hollow mandrel rotatable on an axis, the mandrel having a supported end and a projecting end. A lead screw advances a carriage having a plurality of extruding rolls directed radially inward toward the axis of rotation of the mandrel. The power supplied to rotate the mandrel is resisted by the rolls. In the present invention, the rolls have pressure applying surfaces to extrude in the same direction as the travel of the roll carriage station, from the projecting end of the mandrel and to its supported end. At the projecting end of the mandrel are means, such as an annular resilient sealing ring, to engage the billet and apply torsional force to it. Through the hollow of the mandrel and a valve near its supported end, air is evacuated from the center of the sealing ring.

Collar means grasps the billet at its other end nearest the supported end of the mandrel. A ring-like bearing mount, positioned around and spaced radially from the mandrel, includes an inner bearing mounted to the collar means, and an outer rotation-permitting bearing to transmit, through the inner bearing to the collar means, a plurality of longitudinal forces equivalent to a single axial force directed toward the supported end of the mandrel. Such axial force is applied to the outer bearing by extensible pressure cylinders aligned parallel to the mandrel axis and spaced at equal radial distances from the axis of the mandrel and at equal arcuate distances from each other. As the roll carriage is advanced by the lead screw, these cylinders apply tension throughout the wall of the billet, to afford the advantages mentioned.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view, partly in elevation and partly in section, showing apparatus embodying the present invention as applied to a conventional tool having a powered mandrel and forming rolls advanced by a lead screw. To the extent that the tool shown is conventional, the drawing is schematic.

FIG. 2 is a view, schematic to the same extent as FIG. 1, taken along line 2--2 of FIG. 1.

FIG. 3 is a sectional view taken along line 3-3 of FIG. 1.

FIG. 4 is a fragmentary prospective view, partly broken away, showing the present apparatus and method in an advanced stage of forming a large-diameter, thin walled tube.

DESCRIPTION OF THE PREFERRED EMBODIMENT The side elevation, FIG. 1 illustrates schematically a conventional type tool generally designated a on which tubular billets may be roll-extruded axially to form thinner walled objects. Such tool a consists generally of a power and gear reducer section b; a mandrel mount having a horizontal axis of rotation d; a pair of horizontal lead screws e parallel to and at each side of the mandrel axis at and powered by the gear reducer section b; elongated horizontal base ways f at floor level parallel to the mandrel axis d; an end post g at the far end of the ways 1'', in which the ends of the lead screws e are supported on bushings h; and a roll carriage generally designated i, supported on base slides j engaged in the ways 1, and advanced by the engagement of internally threaded portions k with the lead screws e.

Three extruding rolls l, spaced at 120 intervals about the axis of rotation d, are directed radially inward toward the axis d by conventional means which permit precise radial adjustment and hold the rolls rigidly in place, so as to apply pressure which locally exceeds the yield stress of the metal to be extruded. Through the roll carriage i, formed about the axis d is a large open throat 2, into which the rolls 1 project. Intricate adjustment provisions for such rolls are conventional and are not part of this invention; therefore they are here shown merely schematically. In the simplified arrangement illustrated in FIGS. 1 and 2, each of the three rolls l is mounted on a short shaft in held in a heavy fork n having a squared shaft portion 0. This passes radially through a guide block 12 set in one of the three radial passages it which extend at 120 intervals through the heavy frame of the carriage i. The outer end of the shaft portion 0 is shown rounded and threaded, to serve as a radially adjustable end portion q. Its threads are engaged by the threads of a rotatable adjustment nut r having an internal wrenching end s. Heavy hollow nut-abutment fittings v are bolted onto the outer walls of the carriage i, to resist radially outward movement of the fork n. While in the simplified example here illustrated, the rolls 1 would be positioned by wrenching the adjustment nuts r through the hollowed fittings v, such machine tools are conventionally provided with means to adjust the rolls 1 simultaneously by powered mechanism according to automatic programs and with other features which are beyond the scope of the present invention.

In the improvement of the present invention, a hollow mandrel having a hardened outer cylindrical surface 11, is supported along the axis d by the mandrel mount 0, at one end hereafter referred to as the supported mandrel end 12. An external mandrel flange 13 at the supported end 12 is bored radially inward, and has a radial airevacuating passage 14 and valve 15 through which communication is established to the hollow interior 16 of the mandrel 10.

In the somewhat rounded end opposite to the supported end 12, referred to hereafter as the projecting end 17, near its outer periphery, is inset a projecting annular resilient sealing ring 20, made of rubber or rubber-like material. When a closed and tubular billet, as hereafter described, is placed on the mandrel 10, air may be evacuated inwardly of the center of the seal 20 and out through the hollow interior 16 of the mandrel 10, the passage 14 and the valve 15.

Between the ways f is located a central horizontal U-shaped slide guide 22, in which is supported a sliding pedestal portion 23 of a large vertical tension-exerting frame generally designated 25. The frame 25 has three force-application lobes, a lower lobe 26 immediately above the pedestal portion 23, and left and right side lobes 27 spaced angularly at 120 spacings from the lower lobe 26 and from each other. To each of the lobes 26, 27 is mounted, on the side opposite to the supported end 12 of the mandrel 10, the elongated piston shaft 28 of the horizontal fluid pressure cylinder 30. The pressure cylinders 30 are mounted in the roll carriage i, spaced at equal radial distances fom the mandrel axis d and at equal angles of 120 from each other. They are aligned parallel to the mandrel axis d, to serve as means to apply three longitudinal forces directed toward the supported end 12 of the mandrel, equivalent to a single force along the axis a.

Because of the stroke length required of them, each cylinder 30 projects a substantial distance beyond the roll carriage i on the side of the post g. At its aft projecting end each is equipped with a pressure relief valve 31, adapted to be preset at a chosen pressure, for example, 750 lbs. per square inch. Through conventional means, oil is supplied to the cylinders 30 under pressure; when such pressure is exceeded in the operation to be described, oil will flow out through the relief valve 31, gradually shortening the amount which the pistons 28 extend from the cylinders 30. The pressure within the cylinders is supplied as forces which pistons 28 exert on the lobes 27 of the frame 25, as shown by the three linear arrows in FIG. 4.

The tension-exerting frame 25 there illustrated has a circular inner periphery 32 formed about the axis d, in which is mounted the outer race of a large ring-like bearing 33, of the type adapted to transmit thrust from the piston shafts 28 to the inner race, to which is mounted a rotating collar 34. The collar 34 has an inner cylindrical surface 35 larger in diameter than the mandrel 10.

Fitted and secured to the collar 34 by bolts is the outwardly flanged end 37 of an extension barrel member generally designated 38, Whose inner diameter is likewise greater than the outer diameter of the mandrel 10. Its flanged end 37 is inwardly supported by a ring-like bushing 39, fitted onto the mandrel 10. The tubular body portion 40 of the barrel 38 is of a convenient length, chosen to accommodate the length of the tubular billet to be formed to the length and positions of the cylinders 30 in the roll carriage i. In thinning by progressive operations as hereinafter described, the barrel to be chosen for the later operations may be of a different length than the barrel 38 chosen for the initial extrusion operation. Instead of changing barrel lengths, provision may be made for adjusting the axial position of the cylinder 30 in the roll carriage 1'.

At the end of the barrel 38 close to the projecting end 17 of the mandrel 10 is another support bushing 39. At that end the barrel has a radially enlarged broad flange 41 having a ring of adjacent rectangular windows 42. In these are fitted wedging blocks 43, shown in cross-section in FIGS. 1 and 2. In FIG. 4 one of the windows 42 is shown without a block. Each block 43 has an inward projecting latching tongue 44. The blocks 43 are held in the windows 42 by bolted-on arcuate plates 45, one of which is shown broken away in FIG. 4. On mounting the billet, a bolted collar 46 is secured to the windowed flange 41. The outer diameter of the collar 46 is sufficiently small to permit its entry into the throat t of the carriage i, so that in forming the rolls I may approach as close as possible to the collar 46.

Each of the extruding rolls 1 has a pressure-applying surface 47 directed, as shown in FIG. 1, to extrude toward the supported end 12 of the mandrel 10. The lead screws e are set to move the carriage i, whose position determines the position or station of forming, in the same direction as surfaces 47 of the rolls l extrude the material.

The method of the present invention will now be described. A billet of extrudable metal is machined to form a tubular billet generally designated 50. FIG. 1 shows such a billet 50 in the course of being extruded during the first extruding operation; FIG. 4 shows it during a later operation, after it has been both thinned and elongated. The billet is preliminarily machined from a rough billet, to provide a closed end 51 which is initially machined to its final internal and external configurations, preferably rounded as shown. The fact that the end 51 is inwardly constricted permits it to engage the billet to the projecting end 17 of the mandrel 10 with a strong frictional force through which the driving torque of the tool is transmitted. Where the end 51 is closed as shown, evacuation of the air inwardly of the sealing ring 20 provides a vacuum fit, by which ample driving torque may be transmitted. The inner wall 52 of the billet 50 is also finally machined before fitting onto the mandrel 10, while its outer wall 53 is machined with lesser accuracy. The initial wall thickness of the billet 50, so machined, is calculated so that the volume of material in that part of its wall available for extrusion will equal the amount of material required for a tube of the final length and wall thickness desired. A portion of the material of the end opposite the closed end 51 is required for grasping by the barrel 38. At this end is machined a circular groove 53.

The several steps of operation will now be described. As will be apparent, the precise order of some of the steps is immaterial; for example, in mounting the billet 50 to the extrusion barrel 38 and mounting it in turn to the collar 34 at the tension exerting frame 25. Preferably, the barrel 38 is put in place on the mandrel 10. Having set the lead screws e to move the roll carriage i toward the supported end 12 of the mandrel and mounted the rolls l with their pressure-applying surfaces set to extrude in that direction; and having lubricated the surface of the mandrel 10, the end of the billet 50* opposite its closed end 51 is fitted over the projecting end 17 of the mandrel 10 and the billet 50 is moved thereon axially, until its closed end 51 engages the projecting mandrel end 17 and presses against the sealing ring 20. During this step, the valve is left open; thereafter the air is evacuated from the center of the sealing ring through the hollow mandrel 10, and the valve 15 is closed. The mounting of the billet 50 to the windowed flange 41 is then completed; the blocks 43 are inserted through the windows 42 so that their tongues 44 engage the groove 53; and the arcuate plates 45 and collar 46 bolted in place. At some convenient time in the order of assembly, the barrel 3 8, on its ring bushings 39, will have been mounted by its flanged end 37 to the rotatable collar 34 of the tension frame 25.

Extruding of the billet 50 is commenced at its closed end 51. The rolls I are positioned radially from the axis d to reduce the billet Wall thickness to a first predetermined amount. As the mandrel 10 rotates and the carriage i is drawn toward the supported end 12 of the mandrel 10, such reduction in wall thickness takes place, as shown in solid lines in FIG. 1. As the carriage i is drawn toward the supported end 12 of the mandrel and the rotation of the mandrel 10 beneath the rolls 1 extrudes the material of the billet 50 between the rolls 1 and the collar 46, the progressing of the carriage i closer to the barrel 38 will tend to increase the pressure within the cylinders The excess pressure will be relieved through the check valves 31 and the piston shafts 28 will gradually recede, thus permitting the rolls l to approach closer to the collar 46. The positions of the parts at the end of the first extrusion operation are shown in the phantom lines in FIG. 1.

To reduce the wall thickness, the material of the billet is stressed in bearing beneath the rolls I, beyond its yield point, to extend itself in whatever direction it may. Since there are only three localized points of roll pressure, resistance is offered to such extension by the adjacent material. As will be recognized, the desired flow of material is axial, to produce a thin-walled tube. Undesirable flows or components of flow include those which are tangential, which would increase the inner diameter, and those which are irregularly local.

How the present invention achieves such desired flow, and avoids undesirable flow, will now be explained. Hydraulic pressure of say 750 lbs. per square inch is supplied to the cylinders 30, to exert a tension force, through the frame 25 on the extension barrel 38 and thus throughout the wall of the billet 50, equal to a single axial force. Were it not for the pressure exerted by the forming rolls I, this force would be reacted at the closed end 51 of the billet. However, the bearing force of the rolls l, acting through the billet 50 and against the surface of the mandrel 10, is so great, especially after the billet wall has been greatly thinned, as to create three points at which much of the tension force is resisted. At these points the tension force draws the flowing material of the billet 50 axially in the direction toward which the forming rolls are moving it. Being so directed by the tension force, the flowing material does not tend to flow tangentially; and hence the danger of diametral increase is overcome. As the driving force supplied to the mandrel 10 rotates in the direction shown in FIG. 4, the extruding pressure of the forming rolls 1 acts on the billet 50 to oppose rotation as three highly concentrated local forces (see the small curved arrows in FIG. 4). Without the tension applying frame 25 and cylinders 30, the thinned wall would be likely to buckle locally as the material yielded locally at the points of forming. I have found, however, that the tension force overcomes this tendency to buckle and form local irregularities.

Depending upon the characteristics of the metal to be extruded, it has been found feasible to so set the rolls 1 as to thin the billet 50 approximately 50% on each operation; on each such thinning, the length over which the rolls act will be approximately doubled. To relieve the stresses from such extreme forming, the tubular article as extruded may be removed and annealed, replaced on the mandrel 10, and again extruded in a progression of operations. The result is a long tube whose inner diameter fits precisely on the mandrel 10, whose wall thickness is uniform and Whose strength has been greatly increased by the cold flow of the repeated extrusion steps. If the article finally to be formed is to be a simple open tube, the closed end 51 and the end grasped by the windowed flange 41 Will then be cut off; but in some applications, as in the making of elongated thin-Walled pressure vessels, the article may be used precisely as formed.

To remove from the mandrel 10, the valve 15 is opened and air pressure is applied through it and the hollow interior 16 of the mandrel 10, to press axially against the tube closed end 51. This removal procedure is particularly advantageous after the final step of forming, to avoid inadvertent damage to the thinned wall.

The new method of this invention does not require the very apparatus illustrated and described. For some purposes, other procedures might be followed using different apparatus. For example, a tubular billet might be mounted onto a barrel attached to the flange 13 at the supported end if the mandrel 10, to apply the driving torque through the barrel; a tension frame having a rotatable collar might be mounted at the opposite side of the carriage i, with the pistons 28 projecting toward it, so as to put the billet in tension in a direction away from the supported end 12 of the mandrel 10; and the direction if carriage movement and the position of the pressure applying surfaces 47 of the rolls 1, reversed. Rolling would then be commenced at the end of the billet near the supported end 12 of the mandrel, at which the driving torque 'Would be applied to the billet. In such an application, as with the apparatus illustrated, the torque would be transmitted through that portion of the billet which had already been thinned by the rolls; and localized stresses at the rolls would be removed by the force applied through the tension frame 25. I Iowever, the apparatus and steps described in detail hereinabove are considered more suitable, especially where the ultimate product to be extruded in progressive operations is an extremely thin walled tube.

Other modifications and adaptions for specific uses will be apparent to those familiar with the problems of the art. Accordingly, the present invention is not to be construed narrowly, but rather as co-extensive with the claims.

' whereby to provide sure transmission of such torsional force from the mandrel to said end of the billet. 6. A tool for forming a tubular metal billet into a relatively thin walled tube, said tool being of the type including I claim:

1. For the purpose of forming a generally tubular billet into an elongated thin walled tube,

the method of using a powered tool, of the type having a cylindrical mandrel whose diameter fits closely ward constriction to and upon the projecting end of the mandrel, 1

within the inner wall of such billet, which mandrel a powered mandrel rotative on an axis and having a is rotatable on an axis under power applied at one supported end and a projecting end,

end of the mandrel and having its opposite end proa pressure roll assembly including a rotation resistjecting, further having a forming station movable ing roll carriage having a plurality of extruding rolls axially by a lead screw and a plurality of pressure 10 directed radially inward toward the axis of the manrolls thereat presented radially inward toward the drel and thereby against the wall of such a billet axis, comprising the steps of mounted thereon, and

setting the lead screw to move the forming station in lead screw means to advance the roll carriage with one direction along the mandrel axis and setting the rotation of the mandrel progressively from the propressure rolls to extrude the billet in the same direc- 5 jecting end of the mandrel toward its supported end,

tion, wherein the invention comprises fitting the billet thel'eovel' and engaging One end P F- pressure-applying surface means on the extruding rolls tion thereof to one end of the mandrel, to extrude in a direction from the projecting end grasping the periphery of the opposite end portion of of the mandrel toward its supported end,

the billet and, while leaving same free to rotate, an means at the projecting'end of the mandrel to engage plying an axial force to put the billet in tension, one end of such billet and apply a torsional force then, applying rotative power to the mandrel and movthereto,

ing the roll station along the lead screw commencing c ll r means to engage and grasp such a billet at its adjacent to the end of the billet so engaged, and other end nearest the supported end of its mandrel,

Simultaneously Pressing the T0118 radially toward the a ring-like bearing mount positioned around and spaced mandrel axis with sufiicient force to extrude the metal radially outw rd from the mandrel, and including of the billet axially and thin it y a desired increment, inner bearing means mounted to said collar means, and and continuing to a point adjacent to the grasped end, outer rotation-permitting bearing means to transmit, then repeating the above Steps on the aXiallY through the inner bearing means to said collar progressively thinned billet until a desired thinness means, an axial force directed toward the supported is reached, end of the mandrel, and y ill each repetition, the torsional force, pplied extensible means to apply to said outer bearing means t t e billet at h g g end P is trahsa plurality of longitudinal forces directed toward the Ihitted through the thinned Well so formed, and supported end of the mandrel and equivalent to a sisted locally at the rolls, and wherein such tension i l i l f force so relieves the concentrated stresses at the rolls h b as h 11 bl i advanced by the lead as to avoid irregularities in formingscrew means, the extensible means applies tension The IIleth0d as defined in claim wherein throughout the wall of the billet, thereby to facilitate the p of pp y a tension force includes applying smooth thinning thereof at the extruding rolls.

such force in a quantity such as to stress the thinned 4O 7 A l as d fi ed i l i 6, h in wall less than the yield stress in tension of the mateh means at the projecting end of th m nd l to rial of which the billet is formed. gage h billet includes 3'. The method as defined in claim 1, which such tubuan annular ili l, d

1&1 billet has a closed and 'Whefei'h means to evacuate air from the center thereof.

the step of engaging to the projecting end of the mang A l as d fi d i l i 6, herein drel illehldes the Steps of forming all annular air-tight the extensible means to apply longitudinal forces to seal between said projecting mandrel end and the id outer bearing me n includes Closed end of the and a plurality of force applying fluid pressure cylinders evacuating from the center of Such annular Sealspaced at equal radial distances from the axis of the 4. T method as defined in Claim wherein 5O mandrel and at equal arcuate distances about said such billet has an inward constriction at one end, and i id cylinders being aligned parallel to the in which mandrel axis. the step of engaging the billet to the projecting end of the mandrel is carried out by fitting the oppo- References Cited site end of the machined billet over the pro- UNITED STATES PATENTS jecting end of the mandrel and moving the b1llet axially ntil said mandrel end engages the inward 1,301,220 4/1919 Brmlfman 7285 constriction f bill t. 2,503,464 4/ 19 Banmster 72-435 5. The method as defined in claim 4, wherein 3,411,334 11/ 1968 Ernestus 7284 said step of engaging the billet includes-sealing its in- 3,433,040 5/ 1969 Lenz 7285 LOWELL A. LARSON, Primary Examiner 

